The engine load on an internal combustion engine in a combine harvester or “combine” may increase as the vegetation density or yield increases in certain zones in a field. Internal Combustion (“IC”) engines are used to power combines under a wide variety of load conditions and must be able to accept sudden changes in load. When the combine is in a transport mode, sudden increases in power and torque are required from the engine when negotiating the terrain between fields. Tillage in field also presents conditions where there are sudden increases in load due to changes in soil condition, where the resistance of the tillage tool increases significantly or the field has steep inclines. Engines of this type are expected to respond to these conditions by increasing output torque with only a small increase in engine load. This increase in torque output is typically referred to as torque rise. Engines with significant torque rise permit the torque curve to be shaped so that the rate of rise is very steep allowing the engine to decrease rpm very little at the same time output torque increases significantly. Engines that are governed use the shape of the governor curve to make the slope extremely steep for operation at or below rated rpm and torque.
Combine harvesters currently have a basic engine torque curve to provide a nominal rated power at a power level approximately 14% below the power capability envelope of the engine. Experience has shown that a 14% power bulge with a 200 RPM droop in engine speed provides good slug handling capability and enhanced drivability for the operator. This enables the use of a power boost for unloading or a power bulge for additional power to handle gradual increases in a load or to handle slugs or other operational overloads without excessive loss of functional engine speed or the stalling of the engine. Traditional engine torque curves for combines have been developed to use this high level of power bulge above the normal rated power in order to enhance the ability of the power train and threshing system to handle the slugs and transient overloads during the harvesting operation. Such an overload may occur when clumps of moist material suddenly enter the threshing system causing higher, short duration overloads.
At the lower power end of the operational spectrum, combines also spend significant time at very light loads, such as idling or traveling down hills. In these cases, the high end torque curves that work well for performance, such as slug acceptance, high threshing loads, unloading grain on the go, etc., do not return as good fuel economy as an engine torque curve optimized for a lower power level operation.
Current EPA regulations (40 CFR part 1039) titled “Control Of Emissions From New And In-Use Nonroad Compression-Ignition Engines”, or referred to as “Final Tier 4” (FT4) are such as to allow higher power diesel engines (>560 kW) to utilize selective catalyst reduction (SCR) units only. Below 560 kW, the specified engine-out emissions are more stringent and in many cases dictate a more aggressive hardware solution. Diesel engines below 560 kW may require exhaust gas recirculation (EGR), diesel particulate filter (DPF) and SCR units to meet the FT4 regulations.
The present inventors have recognized the need for a cost effective, high performance power train for a combine having a peak power over 560 kW.
The present inventors have also recognized that to maintain vehicle drivability in a combine, power bulge is provided so the engine does not stall when the vehicle encounters times of heavy load (crop slugs, going uphill, etc.). About 12-14% power bulge over rated power is desired to be held in reserve to maintain operator drivability. If the engine power held in reserve can be reduced, vehicle productivity and fuel economy can be increased.
The present inventors have recognized that even if the power bulge can be reduced somewhat using a battery electric hybrid system, it would be desirable to reduce IC engine power bulge to near zero. Improvement is desired in battery charging to ensure drivability while reducing IC engine power bulge to near zero. Without the IC engine power bulge, and if the battery pack is not fully charged, the composite vehicle torque-speed curve would change and result in different vehicle drivability to the operator.
The present inventors have recognized that it is desired to modify the system to attempt to capture all of the engine power bulge held in reserve so that full engine power can be used nearly all the time.
The present inventors have also recognized that one of the challenges in using Li-ion batteries is the number of charge/discharge cycles that can be undergone before the battery pack wears out. The present inventors have recognized that a method which reduces the charging/discharging of the battery pack would help extend battery life.